1. Field of the Invention
This invention relates generally to a composition, process, and apparatus, for removing water and mu-oxides of silicon from chlorosilanes.
2. Description of the Related Art
In the manufacture of semiconducting materials and semiconductor devices, dichlorosilane (SiH.sub.2 Cl.sub.2) is widely employed as a silicon source reagent compound for the production of epitaxial silicon films.
In such usage, the gaseous dichlorosilane compound is required to be of high purity, since the presence of contaminants or impurity species therein can render the product semiconductor deficient or even useless for its intended purpose.
Unfortunately, however, dichlorosilane as commercially supplied is characterized by the presence of impurities such as water and various silicon mu-oxides therein. Such impurities must therefore be removed prior to usage of the gaseous dichlorosilane in the semiconductor plant.
The silicon mu-oxide impurities in dichlorosilane may for example include compounds of the formula (SiH.sub.x Cl.sub.3-x).sub.2 O wherein x is a number having a value of from 0 to 3, inclusive, as well as silicon mu-oxide compounds of other stoichiometries, including cyclic compounds. Some illustrative silicon mu-oxide compounds, which may be present in dichlorosilane as impurities, are set out below with respect to their formulae: ##STR1##
The art has proposed to purify dichlorosilane of such impurities by contacting the impurity-containing dichlorosilane with various sorbent materials such as silicas, zeolites, and aluminosilicates. Illustrative of such prior art approaches are the methods and purification materials described in the following patent publications: R. S. Doornbos, "Purification of Chlorosilanes," European Patent Application EP 107784 A1, May 9, 1984; K. Kawasaki and Y. Kitsuno, "Purification of Silane," Japanese Kokai Tokkyo Koho JP 61/48420 [86/48420], Mar. 10, 1986; T. Sugimoto, T. Murayama, and Y. Suzuki, "Purification of Dichlorosilane." Japanese Kokai Tokkyo Koho JP 61/167693A2 [86/167693], July 29, 1986; and T. Sugimoto, T. Murayama, and Y. Suzuki, "Purification of Dichlorosilane," Japan Kohai Tokkyo Koho JP 61/197415A2 [86/197415], Sept. 1, 1986. These methods and purification materials unfortunately have not been found to be highly effective in reducing the concentration of the silicon mu-oxide impurities to the very low levels, e.g., below about 0.1 parts per million (ppm), which are required for the fabrication of satisfactory semiconductor products.
Dichlorosilane may be purified by distillation, but such method is generally equipment-intensive, time-consuming, and expensive.
When water is present as an impurity in the dichlorosilane gas stream, hydrolysis of dichlorosilane may occur, producing hydrogen chloride as a further impurity in the gas stream. This production of hydrogen chloride is however not generally considered critical, except for the fact that metallic components in the process system may be subjected to corrosive action if the hydrogen chloride is accompanied by the presence of water.
Thus, water and silicon mu-oxides are considered to be the critical impurities in dichlorosilane for purposes of its usage as a silicon source reagent in semiconductor manufacturing operations.
It therefore is an object of the present invention to provide a composition, process, and apparatus for the efficient removal of water and silicon mu-oxides from dichlorosilane, to produce a purified dichlorosilane product which is of a suitable purity for semiconductor manufacturing operations.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.